Investigating the three-body fragmentation dynamics of water via dissociative recombination and theoretical modeling calculations

We report an investigation into the three-body fragmentation of a triatomic molecule H₂O via the process of dissociative recombination (DR) of H₂O⁺. At 0-eV center-of-mass reaction energy two competing three-body fragmentation channels are available, both leading to the production of ground state H atoms H(²S) but differing in the excitation state of the O atom fragment: O(³P) and O(¹D). Using time- and position-sensitive detectors in a triple-coincidence experiment, the fragments from the DR reaction are monitored and their momentum vectors and angular distribution recorded. From these data we determine that during the recombination process, oxygen atoms are produced in the ratio of 3.5(0.5):1 for O(³P):O(¹D), and find that the molecular geometry is not conserved and that the available reaction energy is randomly distributed between both hydrogen atoms. Quasiclassical trajectory calculations having the same initial starting conditions as those in the experiment have been carried out using calculated and measured H₂O potential-energy surfaces, together with the knowledge of the various curve crossings, intersections, and estimations of the necessary coupling strengths. The results of these calculations, product state population distributions together with the geometries of the potential surfaces which contribute to the reaction, are compared to those observed in the experiment and allow questions to be answered on the dominance of three-body dissociation